Variable reluctance control means



Aug. 10, 1954 F. s. MACKLEM 5 3 VARIABLE RELUCTANCE CONTROL MEANS filedMarch 15, 1950 Snnentor A sums-Rum? MAC/{LEM Patented Aug. 10, 1954UNITED STATES PATENT OFFICE VARIABLE RELUCTANCE CONTROL MEANS F.Sutherland Macklem, Freeport, N. Y., assignor to Servo Corporation ofAmerica, New Hyde Park, N. Y., a corporation of New York ApplicationMarch 13, 1950, Serial No. 149,235

8 Claims. 1

My invention relates to devices variously known as saturalole reactors,transductors, and magnetic amplifiers for the control of A.-C. power,and is in the nature of an improvement over the circuits disclosed in myco-pending patent application, Serial No. 138,094, filed January 12,1950.

In the prior art, control of A.-C. power has been accomplished by meansof electronic amplifiers or magnetic amplifiers. Electronic ampliherehave the disadvantage that th y require associated D.-C. power supplieswhich are relatively bulky and expensive to construct. Magneticamplifiers have the disadvantage that they rely upon saturation of aferromagnetic core material and therefore are inherently highlynonlinear devices. In particular, they tend to deliver a highlydistorted waveform to their load. when excited with a sinusoidal input.In addition, the inherent non-linearity of magnetic amplifiers makesthem extremely diiiioult to design for optimum performance. Furthermore,magnetic amplifiers introduce relatively long time delays which in someapplications are very serious.

It is, accordingly, an object of the invention to provide an improveddevice of the character indicated.

it is another object to provide an improved means for controlling thepower delivered to an opposed-phase load.

It is also an object to provide improved means for differentiallyresolving two independently variable signals.

It is a further object to provide an improved means for deriving fromtwo input signals, one variable independently of the other, an outputsignal of phase and magnitude reflecting the instantaneous relativedifference between the input signals.

It is a specific object to meet the above objects with an improvedmagnetic-amplifying means which may not depend upon magnetic saturationor of the phenomena associated with saturation.

Other objects and various further features of novelty and invention willbe pointed out or will occur to those skilled in the art from a readingof the following specification, in conjunction with the accompanyingdrawings. In said drawings, which show, for illustrative purposes only,preferred forms of the invention:

Fig. 1 is a simplified circuit diagram showing a control deviceaccording to the invention; and

Figs. 2 and 3 are further circuit diagrams showing applications of theprinciples of the invention to modified arrangements.

Briefly stated, my invention contemplates means for controlling A.-C.power transferred magnetically from a primary coil to a secondary coilby introducing a variable-reluctance in series with the magnetic pathbetween the primary and the secondary. Although the primary secondarywindings may be interchanged as far as input and output signals may beconcerned, in two forms to be described, the primary winding is coupledto two of three legs of a three-legged transformer core in such a waythat fluxes are generated in both these legs in the same direction. Ifthese fluxes are of the same magnitude, and if the secondary isconnected to load and is coupled to the third leg, then the flux willtravel only in the loop which includes the two primary legs. If,however, the flux in one of the primary legs is caused to vary, as bythe introduction of a variable reluctance in series with one of theprimary legs, then the fluxes the primarv legs will be different; a fluxequal to this difference will circulate through the secondary leg, and atransfer of power to the load may be effected. In the third arrangement,the fluxes are caused to flow in opposite directions.

Referring to the schematic arrangement of Fig. l, I show my invention inapplication to a means for controlling the magnitude and phase of powerdelivered to an opposed-phase load 5, which may be part of a reversiblemotor to be driven in one direction at varying speeds, in accordancewith varying amplitudes of voltage of one phase in duced in a secondarycoil 6; the motor 5 may be driven in the opposite direction at varyingspeeds in accordance with voltages of opposite phase induced in thesecondary winding The sec ondary winding 8 may be coupled to one leg lof a three-legged transformer core 8, and in the form shown the outputor secondary leg "2 is the center leg of the core 8. The core 5 mayinclude two other egs 9l G which may both be energized by the sameprimary-winding means, but which, in the form shown, are separatelyenergized by primary coils !ll2, respectively, connected to each otherin series so that they may be energized by a common source 4 of A.-C.power.

The windings iI-l2 are preferably so arranged with respect to each otherthat, when energized by the source 4%, they may each set up fluxes inthe same direction in their respective core legs, and I haveschematically indicated that a flux 1 is set up by the primary coil H inthe left leg 9, while a flux oz of the same direction or polarity is setup by the primary coil I2 in the right leg it. If the magnitudes of thefluxes 1 and 2 should be the same, then flux will tend to circulatethrough a loop defined by the primary legs 9lll to the exclusion of thesecondary or output leg i so that, under such circumstances, no powerwill be transferred to the load 5. If, however, the flux set up in oneprimary leg should be of a different magnitude than the flux set up inthe other primary leg, then a fiux equal to the difference between 1 and2 will be caused to flow in the secondary or output leg with the resultthat the load or motor 5 will be driven in accordance with the magnitudeand sense 'or phase of this difference.

In accordance with a feature of the invention, control of the fluxdiverted to the secondary or output leg 7 may be achieved by introducinga variable reluctance in series with one of the primary paths of thelegs '9H. Thus, if the two primary coils il-l2 were of different size soas to induce different fluxes 12 in their respective legs, and ii avariable reluctance such as a coil is connected to a variable impedanceit were coupled to one or" the primary legs (9), then merely by varyingthe single control impedance (it) one might achieve a range of values offlux e1 extending from 1 less than oz, to 1 equal to oz, to or greaterthan p2. However, in the form shown, I prefer that the impedance in theprimary legs 9-4 G shall be normally the same so that the iiuxes 12normally set up by primary windings ii-l2 may be the same; for controlpurposes, I prefer to employ a control or tertiary winding in serieswith each primary leg, and a winding it on the right leg iii may beconnected to a variable impedance is in the manner which has alreadybeen described for tertiary it on the left leg 9.

In operation, if the control impedance i l equals the control impedanceIt, then the reluctance through both primary legs will be the same,equal fluxes 12 will be induced, and no power will be transferred to theload 5. However, if the control impedance M is made less than thecontrol impedance it, the flux 1 will be less than the ilux 52, and thecenter or output leg l will carry a flux in the direction of the flux452 and of a magnitude representing the difference between the flux c1and the flux oz. The load 5 wil1 then be driven with a voltageproportional to this difference and in a direction or phasecorresponding to the direction of fiow of the fiux c2 through the centerleg l. Conversely, if the control impedance E6 is made less than thecontrol impedance i l, the flux qbz will be less than the flux i, andthe differential then passing through the secondary leg l will efiect atransfer of lie-C power to the load 5 with a magnitude againproportional to the flux difierenee but of a direction corresponding tothe direction or" flow of flux l through the center leg l. Thu it isclear that A.-C. power supplied to the load 5 may be controlled inmagnitude and reversed in phase so as to reflect instantaneousindependent variation of the two control impedances ltl-l6-.

In Fig. 2, I show a modified means for controlling the same type ofdifferential magnetic amplifier which has been described in connectionwith Fig. l. The circuit in Fig. 2 may in all respects resemble that inFig. 1 except for the control means, and I have, therefore, employed thesame numerical designation o1 circuit elements. In the control means ofFig. 2, the magnitude and polarity of ,power delivered to anopposed-phase load 5 may be controlled in accordance with theinstantaneous difference of two steady or slowly varying independentelectrical signals. Control is, however, effected basically in the samemanner, and the variable impedance of a space-discharge device may beemployed in the circuit of each of the tertiary coils ll-l8.

If desired, a single space-discharge device may be connected to eachtertiary coil, but in the form shown I achieve more effective control byutilization of twin space-discharge paths or devices in push-pull ateach tertiary. Thus, in the case of the tertiary winding ll, twotriodes, Or a doubletriode it: as shown, may be arranged with bothoutputs or plates connected to opposite ends of the tertiary windingE'Lwhile the input circuit including the grids and cathodes may beconnected to terminals 2 32l for application of the control signal. Ifdesired, the cathodes may also be connected to the midpoint of thetertiary winding l's', as shown. Similarly, control signals for thetertiary winding 53 may be applied between input terminals 22-23 foranother doubletriode having plate circuits connected to opposite ends ofthe tertiary winding l8 and having cathodes connected to the midpoint ofthe winding 53.

It will be seen that the tube ld-id may act as variable impedances fortheir respective tertiary windings ll--l 8, all in accordance with themagi tude of control signals applied to the input terminals E lll and22-23, respectively, and that the direction and magnitude of fluxinduced in the output leg l and, therefore, the polarity and amplitudeof power delivered to the load 5 may be varied in accordance with theinstantaneous difference in signals applied at the two control inputs2t-2l and 2223.

Even if the polarity of both control signals at 2ii2l and 2223 should bethe same, it will be understood that upon a predominance of the signalat 2b-2l over the signal at 22-23, a motor load it may be driven in afirst direction at a speed proportional to the difference in signalmagnitudes; conversely, if th signal at 22-23 should predominate overthe signal at 2@-2l, then the motor load 5 may be driven in the oppositedirection at a speed proportional to the difference in signalmagnitudes. As long as the input signals are equal to each other, eventhough they may be varying, the motor load 5 will not be energized.

It will be seen that I have described a relatively simple and compactamplifying means utilizing a controlled magnetic coupling. By operatingthe magnetic core material always below saturation, linearcharacteristics be obtained, and the wave form delivered to the load maybe undistorted when excited with a sinusoidal input. My control meansmay efiect selected speed and direction for driving a motor inaccordance with the instantaneous difierential of two mechanicaldisplacements, as may be involved in the setting of control impedances lll6; or the same type motor may be similarly driven in accordance withthe instantaneous difierential between two electrical signals, asapplied to the inputs 2-2l and 2223. My control means is notcharacterized by long time delays, and audio-frequency responses arecompletely practical.

As indicated generally above, primary and secondary windings may beinterchanged as far as input and outputsignals may be concerned. In thecases of the described circuits, this change may be effected uponconnection of winding 6 to an A.-C. source, so that winding 6 is thenutilized as a primary; windings l l--l2 may then be utilized assecondaries, and the desired opposed-phase directional control may stillbe effected in accordance with the instantaneous difference in magnitudeof impedances across the tertiary windings l3--| 5.

This type of reversed usage of the circuits of Figs. 1 and 2 is shown inFig. 3, wherein the source 4 is connected to winding 6, and whereinwindings I Il 2 are connected to windings 3 l32 of a suitableopposed-phase load, such as a splitwinding. motor to be reversiblydriven in accordance with the prevailing signal induced at one of thewindings I |I2. Th only difference between operation according to Figs.1 and 2 and operation according to Fig. 3 will be in the relativedirections of flux in legs 9-l0; in Fig. 3 fluxes 53 and 54 will be inopposite directions, as indicated, but it will be appreciated that thesettings of control impedances l4-l6 may have generally the sam desiredeffect of governing th relative magnitudes of fluxes 3--4 and,therefore, the relative magnitudes of output signals in th windings3l--32. In view of the above-indicated reversibility of function of mycontrol arrangements, the terms primary and secondary, as used hereinand in the claims, will be understood merely to identify a winding or apair of windings, and not necessarily to imply connection to an input oruse as an output.

While I have described my invention in detail for the preferred formsshown, it will be understood that modifications may be made within thescope of the invention as defined in the appended claims.

I claim:

1. In a device of the character indicated, magnetic-core means providingtwo flux-loop paths, primary-winding means linked to both paths forcirculating flux in both said paths, secondarywinding meansdifferentially linked to both paths and disposed for connection to aload, there being equal numbers of secondary-winding turns coupled toboth said paths, whereby said secondary-winding means may respond toenergize the load in accordance with the instantaneous differencebetween fluxes in said paths, tertiarywinding means including separatelike coils each 6 independently linked to a different one of said paths,and separat impedances connected to each of said coils, one of saidimpedances being variable.

2. In a device of the character indicated, a three-legged transformercore, whereby there may be two flux loops common to each other in one ofsaid legs, primary-winding means inductively coupled to said core insuch manner as to set up fluxes in both said loops when excited by asource of alternating voltage, secondarywinding means inductivelycoupled to said core in a manner to respond differentially to fluxes insaid loops, said secondary winding means being electrically independentof said primarywinding means, and control means including two tertiarywindings, each inductively coupled to one of said loops to the exclusionof the other of said loops, separate impedances connected independentlyand directly across said tertiary windings, at least one of saidimpedances being variable.

3. A device according to claim 2, in which each said impedance includestwo space-discharge circuits having outputs connected for push-pulloperation across each of said tertiary windings.

4. A device according to claim 3, in which each said tertiary winding iscenter-tapped and connected to the common pole of the push-pull outputsof said space-discharge circuits.

5. A device according to claim 2, in which said primary-winding means islinked to both loops of said core independently of said common leg.

6. A device according to claim 2, in which said primary-winding means islinked to said core on said common leg.

7. A device according to claim 2, in which said secondary-winding meansis linked to both loops of said core independently of said common leg.

8. A device according to claim 2, in which said secondary-winding meansis linked to said core on said common leg.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,902,466 Ratkovsky Mar. 21, 1933 2,440,984 Summers May 4,1948 2,491,221 Singh Dec. 13, 1949

